Amotosalen-HCI is a proprietary psoralen compound owned by Cerus Corporation, which has been developed for the inactivation of pathogens for the blood transfusion industry. Amotosalen-HCI is used in a photochemical process for the inactivation of pathogens in platelet concentrates and in fresh frozen plasma. AIIogeneic Cellular Immune Therapy (ACIT), another photochemical process requiring Amotosalen-HCI, has been in development at Cerus Corporation for the past 5 years. The program is focused on solving the major unmet need of safety in mismatched stem cell transplantation. ACIT has generated several classic manuscripts and awards from the American Society of Hematology and has been under investigation in the clinic in three trials. The first, "A Phase I Study of Photochemically Treated Donor T-Cell Supplements in HLA Haplotype Mismatched Hematopoietic Stem Cell Transplantation," was first filed with the FDA on 12/30/98. The second, "A Phase 1B Study of Photochemically Treated T-cell Supplements in Unrelated Donor PBSC Transplantation," was filed with the FDA by the National Marrow Donor Program and approved on 9/30/02. The third trial, "Autologous EBV+ Lymphoblastoid Cell Line Treated with Synthetic Psoralen (Amotosalen-HCI) and Ultraviolet A Light (UV Illumination System, Cerus)," has been filed by Johns Hopkins School of Medicine and was approved by the FDA on 61612002. We have received additional requests for new clinical trials using Amotosalen Photochemically Treated cells for the improvement of stem cell transplantation, for the development of vaccines, and for facilitating photophoresis. ACIT technology fulfills an unmet need. ACIT technology needs financial support for its aggressive development, and unfortunately the present business climate has eliminated the possibility that there will be sufficient internal support from Cerus Corporation. This Phase I application requests the funds required for the development of a GMP formulation of Amotosalen-HCI at Cerus Corporation. The previously used formulation for prior ACIT clinical studies is no longer manufactured and can no longer be supported. This application requests the funds needed for a crossover study which will validate a new formulation of Amotosalen-HCI for use in clinical studies not directed at the pathogen inactivation market. Extensive stability studies will be required to determine the adequacy of the Cerus Amotosalen-HCI.